This invention relates to jaws for chucks, and more particularly to the shape of the threads used on such jaws.
Chucks are widely used for releasably holding tools of various sizes (e.g., drill bits of various diameters) in the machinery (e.g., a drill press) which operates the tool. A very common type of chuck has (1) a main body, (2) three longitudinal jaws which are mounted in the main body so that they are equidistantly spaced about and inclined toward a longitudinal axis of the main body, and (3) a nut mounted on the main body for rotation about the longitudinal axis of the main body. The nut has an internal thread which forms a frustoconical helix concentric with the longitudinal axis of the main body. This thread engages a thread segment on each of the jaws so that rotation of the nut causes each jaw to move parallel to its longitudinal axis and therefore toward or away from the longitudinal axis of the main body, depending on the direction of rotation of the nut. In this way the jaws can be made to grip or release a tool (e.g., a drill bit) which is coaxial with the longitudinal axis of the main body.
A problem sometimes encountered with chucks of the foregoing type is that rotation of the nut applies a frictional force to the jaw threads which tends to cause each jaw to rotate about its longitudinal axis. Because the threads on the jaws are only thread segments, they have end edges which can dig into the threads on the nut when the jaws are thus rotated about their longitudinal axes. This resists or impedes further rotation of the nut, thereby interfering with smooth operation of the chuck and also possibly reducing the gripping force applied to the tool by the jaws. Although this effect may be noticeable in both directions of nut rotation, it tends to be a more serious problem when the nut is rotated in the tool chucking direction rather than in the tool unchucking direction because as the tool is gripped, the above-mentioned frictional force tending to rotate the jaws about their longitudinal axes increases.
In view of the foregoing, it is an object of this invention to improve chucks of the type described above.
It is a more particular object of this invention to provide improved configurations for the thread segments on chuck jaws of the type described above which reduce or eliminate the problem of edges digging into the threads on the associated chuck nut.